Porcine Actinobacillus suis Infection – NAVLE Study Guide

Overview and Clinical Importance

Actinobacillus suis is a Gram-negative, NAD-independent, non-motile coccobacillus that colonizes the nasopharynx and palatine tonsils of healthy pigs. While often considered a commensal organism, A. suis has emerged as a significant pathogen in high-health status (HHS) herds and specific pathogen-free (SPF) pig populations. The disease has become increasingly important since the 1980s with the advent of segregated early weaning (SEW) practices and management techniques that minimize neonatal exposure to endemic pathogens.

The organism produces similar toxins (ApxI and ApxII) to Actinobacillus pleuropneumoniae (APP), making differentiation based on lesions alone extremely difficult. However, unlike APP, A. suis causes septicemia with multiorgan involvement and typically affects fewer than 10% of pigs in a population.

Etiology

Organism Characteristics

Epidemiology

Transmission and Risk Factors

A. suis is considered an "early colonizer" of neonatal pigs, with transmission occurring through direct contact with carrier animals. The organism colonizes the upper respiratory tract and can be found in the tonsils and nasal cavity of 30-50% of healthy pigs. Carrier sows introduce the bacterium to herds, and the organism can also be found in the reproductive tract of healthy sows.